The present invention relates to a travel control apparatus for a motor vehicle or car. More particularly, the invention is concerned with a travel control apparatus which is capable of controlling not only a cruise speed and a creep speed but also the speed of a vehicle which is following a preceding car with a proper distance thereto so as to assure safety in driving.
For vehicle speed control, there have been known a cruise control apparatus which maintains the speed of a vehicle constant at high speeds and a creep control apparatus which keeps the vehicle speed constant at low speeds. The creep control apparatus is especially advantageous when travelling in congested traffic for long periods of time, when parking a vehicle in a garage, or when passing another vehicle along a narrow road. However, the vehicle speed control systems known heretofore suffer from a disadvantage that the driver can not freely control the vehicle speed which is set in advance.
For a better understanding of the background of the invention, a vehicle travel control apparatus known heretofore will first be described in detail by referring to FIG. 15. An internal combustion engine, generally denoted by reference numeral 1, is equipped with an intake pipe in which a throttle valve 11 is mounted for adjusting or regulating the output torque of the engine. The opening degree of the throttle valve 11 is sensed by a throttle opening sensor 14. The engine 1 has an output shaft which is coupled to a transmission 2 such as a torque converter. A gear change actuator 4 is installed in association with the transmission 2 for changing the gear ratio thereof. A vehicle speed sensor 6 is provided for sensing the vehicle speed on the basis of the rotational speed of an output shaft of the transmission 2. Output signals from the throttle opening sensor 14 and the vehicle speed sensor 6 are input to a transmission controller 22 which is adapted to determine the gear ratio of the transmission 2 on the basis of these signals to thereby control the gear change actuator 4. Further provided are an accelerator pedal 17, a brake pedal 18, a brake lamp 10 and a brake system 23 for applying a braking force to wheels of the vehicle. For the purpose of controlling the vehicle speed at a constant level, a speed controller 24 is provided which controls a throttle actuator 25. Reference numeral 26 denotes a cruise speed setting switch for setting the cruise speed of the vehicle, and reference numeral 27 denotes a set speed changing switch for changing the cruise speed as set by the switch 26.
Operation of the above-mentioned vehicle travel control apparatus will be described below. When the driver depresses the accelerator pedal 17, the throttle valve 11 is opened, as a result of which the output torque of the engine 1 increases. In other words, the vehicle speed can be adjusted or regulated by controlling the opening degree of the throttle valve 11 through the accelerator pedal 17. The transmission 2 serves to transmit the output torque of the engine 1 to the driving wheels of the vehicles with a reduction ratio which is arithmetically determined by the transmission controller 22 on the basis of the output signals of the throttle opening sensor 14 and the vehicle speed sensor 6. The output of the transmission controller 22 is supplied to the gear change actuator 4 which serves to set the gear ratio of the transmission 2 at a value determined by the transmission controller 22.
When the driver desires to cruise the vehicle at a current speed, he or she operates the speed set switch 26. In response, the speed controller 24 stores the current vehicle speed and controls the throttle actuator 25 such that the current speed is maintained by holding the current opening degree of the throttle valve 11. For releasing the vehicle from the constant speed mode, the driver depresses the brake pedal 18. Depression of the brake pedal 18 is detected by the speed controller 24 which then issues to the throttle actuator 25 a command to fully close the throttle valve 11. At the same time, depression of the brake pedal 18 actuates the brake system 23 while lighting the brake lamp 10 to send a message of deceleration to a succeeding car running behind the vehicle of concern. When the vehicle is to be restored to the set speed, the driver accordingly manipulates the switch 26. Further, when the set speed is to be changed during travel of the vehicle, the speed change switch 27 is operated to accelerate or decelerate the vehicle speed.
FIG. 16 shows another known vehicle travel control apparatus. As can be seen from this figure, the known apparatus differs from the one shown in FIG. 15 in that an obstacle detector 30 and an alarm 31 are additionally provided. When an obstacle is detected by the obstacle detector 30 during travel of a vehicle, an obstacle detection signal is supplied to the speed controller 24 to thereby trigger the alarm 31 which then generates an alarm to alert the presence of the obstacle to the driver.
The vehicle travel control apparatuses described above suffers from various disadvantages. First, a cruising command is generated through manipulation of the speed setting switch 26 by the driver, and in order to change the cruising speed once set, the driver is required to manipulate the speed change switch 27 or the driver has to once clear the cruising mode and set again that mode with a new cruising speed. Thus, troublesome manipulations are imposed on the part of the driver, which is obviously undesirable from the view point of safety in driving. Furthermore, because only the output torque of the engine is controlled, such an unwanted situation may happen that the engine output torque becomes insufficient for uphill travel or the speed adjustment becomes impossible in the course of downhill travel. Besides, at a very low speed, the travel control itself will be rendered impossible.
It must further be pointed out that the running speed of the vehicle can be maintained unchanged even when the vehicle is approaching an obstacle such as a preceding car, thus causing a fear of collision.